In the automatic steering device and veer-off-the-lane alarming device of the ITS, a deviated amount from the lane is frequently required for detecting a vehicle running on the lane because the deviated amount tells the driver whether the vehicle keeps running on the lane or drifts outside the lane. The lane markers are embedded in respective lanes of roads with given intervals as indicators from which veer-off from the lane and a skid amount from the lane can be found. The relative relation between the lane marker and vehicle is detected, thereby telling the movement of the vehicle.
FIG. 1 illustrates a conventional sensing device for detecting an attitude of a vehicle utilizing lane markers. Lane markers 52 are set on each lane in a road with given intervals. Vehicle 51 has two lane-marker detectors 53 and 54 on its front for detecting lane markers 52, i.e. detector 53 on the front left of the vehicle for detecting lane markers on the left-hand side, and detector 54 on the front right of the vehicle for detecting lane markers on the right-hand side. When detecting lane marker 52, detector 53 outputs FL, and when detecting lane marker 52, detector 54 outputs FR. If vehicle 51 deviates to the right with regard to the lane, FL becomes greater than FR. If vehicle 51 deviates to the left with regard to the lane FR becomes greater than FL.
Skid-detector 55 finds skid amount TE from the following equation. EQU TE=K1.times.(FL-FR)
where K1 is a proportionality constant.
When TE takes a positive value, the vehicle shifts to the right, and when TE takes a negative value, the vehicle shifts to the left. An absolute value of TE is proportional to the skid amount.
The construction discussed above allows the conventional sensing device to detect lane markers 52 set on the road by lane-marker detectors 53, 54 disposed on both sides on the front of the vehicle, thereby finding the skid amount including a skid-direction of right or left.
This construction of the conventional sensing device; however, only measures a skid amount, and other apparatus including cameras and speed sensors are essentially required for monitoring the movement including an attitude and speed of the vehicle.
In addition to this problem, detectors 53, 54 disposed only on the front of the vehicle results in detecting a different amount from an actual skid amount when the vehicle takes an attitude different from the road travelling direction.